Process of carbonizing metals



ay 1933= b. v. IREDELL PROCESS OFCARBONIZING METALS I Filed Jan. v 25 1929 INVENTOR C.\/ IREDELL 'AT'TORNE Patented May 16. 1933 UNITED STATES wears PATENT OFFICE CHARLES V. IREDELL, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA PROCESS OF GARIBONIZING- METALS Application filed January 25, 1929. Serial No. 334,909.

This invention relates to the art of carbonizing metal surfaces and more particularly relates to a method of carbonizing nickel or other metals which are used as the grid and plate materials in electron discharge devices.

In electron discharge devices such as radio tubes, power tubes, etc., it is customary to apply to the anode surface an adherent coating of carbon to augment the heat emissivity or the heat dissipating property of the material of the anode. In electron discharge devices utilizing one of the so-called oxide coated type cathodes there is a tendency for the alkaline earth metal oxides comprising the cathode coating to sputter and be deposited upon the grid and the anode and when considerable power output is employed it is often found that the anode and grid electrodes become iiu-andesced sufficiently for the sputtered or deposited alkaline earth metal oxides to become emitters of electrons. It has also been determined thatin electron discharge devices utilizing other type hot cathodes and employing extremely high anode or plate voltages the grid electrode becomes sufiiciently incandesced by electron bombardment to substantially emit electrons.

It is customary to eliminate the tendency of the anode and grid electrodes to emit electrons under the above described conditions by coating these parts with a closely adherent carbon coating as the carbon coating not only prevents the emission of electrons due vice. The carbon coating must also be strongly adherent to the metal surface and preferably entirely covering the same.

The physical characteristics of deposited carbon varies with the method of depositing it. In general, that deposit which is best suited for radiation of heat is most satisfac- 'tory for the purpose of this invention.

It has been proposed heretofore to effect the deposition of the carbon by heating the metal body to elevated temperatures in hydrocarbon gases. It has also been proposed to facilitate the deposition of carbon under these conditions by first oxidizing the surface of the metal body and then heating to heated hydrocarbon gas facilitates the decomposition of the hydrocarbon. gas and deposition of the carbon upon the metal surface.

It is customary in the art to carbonize the metal sheet comprising the anode or.

plate material prior to forming or shaping the anode. It is also customary to carbonize the grid wires prior to forming the grid, as in this way the two stepsof oxidizing followed by-carbonizing may be conducted consecutively'and in a continuous manner. It is essential for the pure carbon coating thus obtained to be strongly adherent to the metal base and substantially not disturbed or removed by thesubsequent forming operations as it is obvious that itj-Wou-ldbeinexpedlentl to repeat a carbonlzingoperatlon to replaceto the relatively high temperature to which it must be heated before such emission may be obtained from the carbon surface but the black surface obtained thereby increases the heat radiating ability of these metal parts and decreases the operating temperatures at any given output current.

or to impart a carbon coatingffollpwing the I l 5" forming operation.

It is also essential for the "successful'fu and application of the formed or shaped car-1 bonized sheet or wire, (that is plate (anode) or grid (control) electrodes), that the metal body and the carbon coating be substantially freed of deleterious gaseous and intermetallic compounds subsequent to the forming or Shaping operation and prior to the utilization of the same in the electron discharge devices.

It is one of the objects of this invention to provide an improved method of carbonizing metal surfaces whereby a closely'adherent substantially pure carbon surface is obtained.

It is another object of this invention to rovide a substantially pure adherent gas ree carbon coating upon cooperating electrodes in an electron discharge device.

It is another object of this invention to improve the method of depositing carbon upon metal surfaces.

Other objects and advantages will become apparent as the invention is more fully disclosed.

In accordance with the objects of my invention I have determined that I" may improve the carbonizing step of the hereinbefore mentioned rior art process of carbonizing metal sur aces, through the addition to the carbonizing hydrocarbon gas heretofore employed of a proportion of the vapor of a liquid hydrocarbon such as petroleum ptiliier, petroleum naptha, benzine and the I have also determined that after coating the metal surface and forming the same to desired shapes, such as plate or grids by the method hereinbefore mentioned I may further improve the formed article by subjecting the same to a heat treatment step at elevated temperatures, in a continuously maintained high vacuo, whereby all or substantially all the deleterious impurities introduced by the said forming operation, such as oxides, greases, etc., and the adsorbed or absorbed gas content of the metal body and carbon coating are substantially removed or rendered substantially non-decomposable under subsequent heat or electronic dissociation effects.

By this general improved process I .am enabled to produce anode or grid articles for use in electron discharge devices with a minimum of shrinkage loss and a maximum in material and operating efiiciency.

As a specific embodiment of the application of this invention, the invention will be described with respect to the forming of carbonized grid electrodes and reference should be made to the accompanying drawing wherein:

Figure 1 shows a side elevational view partly in cross section of the apparatus employed in the continuous oxidizing and carbonizing steps of the process of carbonizing nickel wire which is subsequently to be formed into grids for use in electron discharge devices; and

Figure 2 shows partly in crosssection the vacuum apparatus may employ in the third or degasifying step of my process.

As may be-noted in Figure 1, the wire 1 which is to be carbonized is wound on the unwinding head 2, from which it passes over a movable wheel contact 3, electrically connected by spring contact 4 to any convenient electrical energy supply source such as the battery 5 herein indicated. The wire 1 is then passed vertically downward through oxidizing furnace 6 which may be an ordinary glass or iron tube movably mounted in position as shown and from thence into carbonizing chamber 7 maintained in close relation thereto and which may be made from an ordinary iron tube rigidly mounted in position as shown and thence over a second Wheel contact 8 entirely enclosed in box mounting 27 and electrically connected by spring contact 9 back to the other side of battery 5 over Variable resistance 10 connected in series therewith. The current and therefore the temperature of the wire, may be controlled by the variable resistance 10. From the second contact the wire is conducted to winding head 11, actuated by mechanism not shown.

The carbonizing gas utilized in the carbonizing chamber 7 which comprises the main feature of my invention, is substantially obtained by passing any hydrocarbon gas, such as acetylene, which may be obtained from a compressed source, such as indicated by cylinder 12, through a liquid hydrocarbon, such as petroleum ether. The hydrocarbon gas is conducted by conduit 13 from the cylinder 12 to the bottom of chamber 14:, which is filled to an appreciable height with a liquid hydrocarbon 15 such as petroleum ether petroleum naptha and the like. The gas ubblcs released by conduit 13 in chamber 1 1 passes out of the chamber through conduit 16, the volume or pressure thereof being controlled by How meter 17, and is then passed into the carbonizing chamber 7. Gas exits from the carbonizing chamber 7 are provided at the entrance orifice 18 and exit orifice 19 of wire 1 being carbonized.

A siphoning means for replenishing the liquid hydrocarbon in chamber 14 is shown in Figure 1, wherein chamber 20, siphonically connected by connection 21, is filled from an external source with liquid hydrocarbon as desired through opening 22.

In Figure 2 the apparatus 1 may employ in performing the third or degasifying step of my process is shown, with the vacuum chamber 23 in position in a furnace, winch may be heated in any convenient manner such as by wire wound resistance electrical inches) nickel wire for use in forming grid .second contact wheel 8 and thence to winding head 11.

Suitable'adjustment is made in variable resistance 10 of the electrical circuit from current supply source indicated as battery 5, to incandesce the-nickel wire stretched between the two contact wheels 3 and 8 to give a wire temperature which will suitably affect the decomposition of the hydrocarbon atmosphere and deposition of the carbon upon the surface thereof in the desired condition.

For this size wire I prefer to limit the length of wire exposed to the oxidizing conditions in furnace 6 to approximately 11 to 12 inches, and the length of wire within the carbonizing furnace 7 to approximately 35 to 36 inches, or approximately 3. times the length that is exposed to the oxidizing conditions. I find this a good general rule to follow as I may consequently regulate or vary the speed of the wire through these furnaces and the rate of hydrocarbon gas flow into the carbonizing chamber with greater ease and uniformity in result if some such standard relationbetween the oxidizing and carboniz ing operations is established. With 008 inch nickel wire I have found that the required current to give the requisite temperature in approximately 48 inches incandesced length will vary from 2.85 to 3.0 amperes at 40 to 50 volts.

Inasmuch as there is no accurate means available to measure the actual wire temperature within the carbonizing chamber an approximate estimate thereof only may be made. It is believed that the temperature is approximately 800 C. to 1000 C. but reference hereafter will only be made to elevated temperatures rather than definite temperatures.

With this size wire the inside diameter of either the oxidizing chamber 6 or the carbonizing chamber 7 does not need to be over 1 1, inches and the carbonizing gas flow therethrough does not need to exceed 0.10 cu. ft. per hour although it may be varied from .05 cu. ft. to 0.3 cu. ft. per hour without deleterious results. With this gas flow range bubbling through petroleum ether having a specific gravity approximating .620 or petroleum naptha specific gravity approximating .680 (at 20 to 30 C.) the amount of liquid hydrocarbon vapor carried along is sufficient to effect the desired amount of carbonization on the heated wire surface. The wire speed through the furnaces may be varied from 2 to 5 ft. per

minute but I prefer to maintain a constant speed closely approximating 4 ft. per minute. Under these conditions a carbonized wire of approved appearance is obtained having a heav adherent velvety black car bon coating which is extremely resistant to being removed during the forming opera tion.

' The carrier hydrocarbon I prefer to employ is acetylene which may readily be obtained upon the market in a high state of purity compressed into cylinders. Whereas I specifically prefer acetylene gas, other hydrocarbons of the acetylene series which are gases at room temperatures may be utilized if desired, provided they may be obtained in a sufliciently pure condition and substantially free from deleterious volatile impurities such as sulfur, arsenic and phosphorous compounds which subsequently deleteriously reactwith and effectively destroy the electron emissivity of associated hot cathodes in an assembled device.

Other liquid hydrocarbons than those specified may be utilized including those of the parafline series having relatively high boiling points 90 to 150 C. or higher, such as kerosene, and I may evenaugment or increase the vapor pressure of said liquid hydrocarbons by the application of heat either to the liquid hydrocarbon or to the carrier hydrocarbon gas.

Many variations and departures of this specific embodiment or description may be made without essentially departing from the nature of my invention.

After the incandesced wire has traversed the length of the two furnaces, oxidizing and carbonizing respectively, it is wound upon winding head 11, Figure 1.

The carbonized wire is then wound upon usual manner following which the formed grid is subjected to the third or degasifying step of my process.

As above mentioned, I have found that such carbonized metal bodies tenaciously retain gases which are subsequently difficult to remove when the formed metal parts are put through the usual degasification step in the manufacture of electron discharge devices. I therefore take the formed grids .and place them in nickel or molybdenum boats and insert them in a vacuum chamber such as indicated in Figure 2. The particular apparatus I employ in this step is substantially comprised of a calorized iron tube 23 approximately 5% inches inside diameter. hermetically sealed at one end and connected at the other end in any suitable manner to a vacuum pumping system. There are many Ways ofaccomplishing this general result and the apparatus disclosed in Figure 2 is just illustrative of one method, which gives ready means of inserting and removing the treated degasified grids. The vacuum chamber and the enclosed grids are then heated to 850950 C. in any suitable manner such as by gas or oil burners or asincomposition of the liquid hydrocarbon vapor in association with the hydrocarbon gases is more graphitoidal in nature where it contacts with the metal surface and appears to be overlaid with a velvety black amorphous carbon coating which is substantially less susceptible to gas absorption than the carbon coating heretofore obtained by decomposition of gaseous hydrocarbons alone such as casing head gasoline. The degasified carbonized metal grids may be re-expose d to atmospheric gases Without the reabsorption of deleterious amounts of difliculty removable gases, and may be incorporated in electron discharge devices in the usual manner and will readily give up this adsorbed gas content upon heating by induction in vacuo.

By the practice of the special carbonizing gas mixture of my invention I am substantially able to produce a superior coating to that heretofore obtained wherein the metal surface is coated with substantially pure carbon firmly and adherently cemented to the metal surface by an interposed metallic carbide layer, and from thismaterial I am e11- abled to produce without deleterious loss or destruction of the carbon coating, formed and shaped articles such as grid electrodes which when subjected to the degasification step of my invention provides a finished carbon coated article which evidences superior qualities from a manufacturing, assembling and operating standpoint from what has heretofore been prepared.

Although I have specifically described my invention with respect to the carbonizing of nickel wire for forming the grid electrodes, it is obvious that it could require but little modification to adapt the process to continuously carbonizing sheet metals or carbonizing other wires, such astungsten, molybdenum, nickel alloys and slmilar refractory metals useful in an analogous manner or for the carbonization of formed metal bodies, and such variations and modifications are anticipated as may fa'll'within the scope of the following claims:

What is claimed is:

1. The process of carbonizing the surface of nickel which comprises first producing an oxidized surface thereon and then exposing the oxidized metal at elevated temperatures to the action of a-hydrocarbon gas of the acetylene series containing a proportion of the vapor of a petroleum ether.

2. The method of coating nickel wire with an adherent carbon coating which comprises initially oxidizing the surface of said nickel wire and then subjecting the wire at elevated temperatures to the action of acetylene gas containing a proportion of the vapor of the petroleum ether.

3, The method of forming an adherent carbon coating on nickel surfaces which comprises initially oxidizing the surface and then subjecting the oxidized surface at elevatedtemperatures to the action of acetylene containing a proportion of the vapor of a liquid hydrocarbon of the parafline series.

4. The method of forming an adherent carbon coating on nickel surfaces which comprises initially oxidizing said surface and then heating said oxidized metal body to approximately 800 C. to 1000 C. in an atmosphere of acetylene containing a proportion of the vaporof a liquid hydrocarbon of the parafline series.

5. The method of forming an adherent carbon coating on nickel surfaces which comprises initially oxidizing said surface and then heating said oxidized metal to approximately 800 to 1000 C. in an atmosphere of acetylene containing a proportion of the vapor of petroleum ether.

In testimony whereof, I have hereunto subscribed my name this 23rd day of J anuary 1929.

CHARLES V. IREDELL. 

